Introduction
Defect of memory is one of the most common cognitive disorders related to aging [1]. Until 1990, few studies investigated cognitive impairment in the stage before the diagnosis of Alzheimer’s disease, while subsequent studies focused on the pre-disease or prodromal stage of Alzheimer’s disease [2, 3]. The concept of mild cognitive impairment (MCI) has emerged significantly over the past two decades and is defined as the intermediate stage between the cognitive changes of normal aging and dementia. In the elderly with amnestic MCI, who are at risk of developing Alzheimer’s disease, the impaired ability to learn and remember new information, especially verbal episodic memory impairment, is one of the most important cognitive dimensions related to age that deteriorates at a faster rate [4, 5]. In 1987, Delis et al. added a recognition discriminability (RD) index to the first edition of the California verbal learning test (CVLT), where the hit rate is compared to the number of false-positive errors [3]. In addition, response bias (RB) index was added to the CVLT, which is related to the individual’s tendency to give “yes” or “no” answers, regardless of the type of stimulus. The Shiraz verbal learning test (SVLT), like this test, use the yes/no answering method (16 words from list A and 32 false-positive words) in the memory recognition part to measure the recognition discriminability index and response bias index [6, 7]. Since it seems that in-depth investigation of recognition memory patterns in healthy elderly and those with MCI can help in the early diagnosis of cognitive impairment and the onset of Alzheimer’s disease, the present study aims to compare the RD and RB in the SVLT between healthy elderly and those with amnestic MCI and Alzheimer’s disease.

Methods
This is a descriptive cross-sectional study that was conducted from May to December 2021. The sample were 190 older people ranged 60-89 years in three groups of Alzheimer’s disease (n=61), amnestic MCI (n=60), and healthy (n=59). The criteria for entering the elderly group with Alzheimer’s were the diagnosis of Alzheimer’s or cortical dementia (mild to moderate) based on MRI and the diagnostic and statistical manual of mental disorders (DSM-5) criteria, as well as neuropsychological tests, SVLT, and mini-mental status examination (MMSE), no psychiatric disorders such as major depressive disorder, no neurological diseases other than Alzheimer’s (such as Korsakoff’s and Huntington’s disease), and no aphasia. Those in the amnestic MCI groups were selected based on Patterson & Clarfield’s theory where the inclusion criteria are: Subjective memory complaint (score between -1 and -1.5 standard deviations from the mean in SVLT subscales), normal daily life activity, normal general cognitive function, abnormal memory function, no dementia (cortical or subcortical), no psychiatric disorders, and no aphasia.
Data collection tools were SVLT and MMSE. The SVLT has acceptable psychometric properties in Persian form. Rahmani et al. [8], examined its test-retest reliability on 183 healthy individuals and the results showed that the correlation was in the moderate-to-high range (29-94 in the main variables of the SVLT). In the SVLT, two indices are used derived from the “signal detection theory”, including RB and RD. The MMSE, which has a cut-off point of 21, a sensitivity of 90% and a specificity of 84% in Iranian population [21], is a tool to screen for cognitive disorders. In this study, descriptive statistics, one-way ANOVA, and Scheffe’s post hoc test were used to analyze the data in SPSS software, version 19.

Results
According to the results of one-way ANOVA, no significant difference was observed between the three groups in age and education (P=0.42 and P=0.21, respectively). In terms of cognitive performance, the results of MMSE showed that patients with Alzheimer’s disease and amnestic MCI had significantly lower performance (P<0.001) than healthy older people. The Mean±SD of RD domains (general, semantic, source, and new) in Table 1 showed that the healthy group had higher scores compared to the two groups of Alzheimer’s and amnestic MCI, and they were able to discriminate more correctly in all RD domains (P<0.001).


The results of Scheffe’s post hoc test also showed that there was a significant difference between all pairs of groups (P<0.001). Table 1 shows the Mean±SD of the RB variable for the three groups. The results of one-way ANOVA showed a significant difference among the three groups (P<0.001). The results of Scheffe’s post hoc test showed a significant difference between the Alzheimer’s group compared to the healthy group and amnestic MCI group (P<0.001), but there was no significant difference between the amnestic MCI and healthy groups.

Conclusion
There is an impaired recognition memory in Alzheimer’s disease and amnestic MCI. The SVLT, by evaluating the recognition memory performance, can be used to screen people with Alzheimer’s disease and amnestic MCI before the clinical stages are fully revealed.

Ethical Considerations
Compliance with ethical guidelines
This study was approved by the Ethics Committee of the University of Social welfare and Rehabilitation Sciences (Code: IR.USWR.REC.1400.140)

Funding
This work was supported financially by the Student Research Committee of the University of Social Welfare and Rehabilitation Sciences (Grant No.: 2625).

Authors' contributions
The authors equally contributed in the preparation of this article.

Conflicts of interest
The authors declared no conflict of interest.


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